/**
* Get the look angle for the observers position to the object
* @param[in] eci the object to find the look angle to
* @returns the lookup angle
*/
public CoordTopocentric GetLookAngle(Eci eci)
{
/*
* update the observers Eci to match the time of the Eci passed in
* if necessary
*/
Update(eci.GetDateTime());
/*
* calculate differences
*/
Vector range_rate = eci.Velocity() - m_eci.Velocity();
Vector range = eci.Position() - m_eci.Position();
range.w = range.Magnitude();
/*
* Calculate Local Mean Sidereal Time for observers longitude
*/
double theta = eci.GetDateTime().ToLocalMeanSiderealTime(m_geo.longitude);
double sin_lat = Math.Sin(m_geo.latitude);
double cos_lat = Math.Cos(m_geo.latitude);
double sin_theta = Math.Sin(theta);
double cos_theta = Math.Cos(theta);
double top_s = sin_lat * cos_theta * range.x
+ sin_lat * sin_theta * range.y - cos_lat * range.z;
double top_e = -sin_theta * range.x
+ cos_theta * range.y;
double top_z = cos_lat * cos_theta * range.x
+ cos_lat * sin_theta * range.y + sin_lat * range.z;
double az = Math.Atan(-top_e / top_s);
if (top_s > 0.0)
{
az += Global.kPI;
}
if (az < 0.0)
{
az += 2.0 * Global.kPI;
}
double el = Math.Asin(top_z / range.w);
double rate = range.Dot(range_rate) / range.w;
/*
* azimuth in radians
* elevation in radians
* range in km
* range rate in km/s
*/
return(new CoordTopocentric(az, el, range.w, rate));
}
/**
* Constructor
* @param[in] geo the observers position
*/
public Observer(CoordGeodetic geo)
{
m_geo = new CoordGeodetic(geo);
m_eci = new Eci(new DateTime(), geo);
}
/**
* ructor
* @param[in] latitude observers latitude in degrees
* @param[in] longitude observers longitude in degrees
* @param[in] altitude observers altitude in kilometers
*/
public Observer(double latitude, double longitude, double altitude)
{
m_geo = new CoordGeodetic(latitude, longitude, altitude);
m_eci = new Eci(new DateTime(), m_geo);
}
public static DateTime FindCrossingPoint(CoordGeodetic user_geo, SGP4 sgp4, DateTime initial_time1, DateTime initial_time2, bool finding_aos)
{
Observer obs = new Observer(user_geo);
bool running;
int cnt;
DateTime time1 = new DateTime(initial_time1.Ticks());
DateTime time2 = new DateTime(initial_time2.Ticks());
DateTime middle_time = null;
running = true;
cnt = 0;
while (running && cnt++ < 16)
{
middle_time = time1.AddSeconds((time2 - time1).TotalSeconds() / 2.0);
/*
* calculate satellite position
*/
Eci eci = sgp4.FindPosition(middle_time);
CoordTopocentric topo = obs.GetLookAngle(eci);
if (topo.elevation > 0.0)
{
/*
* satellite above horizon
*/
if (finding_aos)
{
time2 = middle_time;
}
else
{
time1 = middle_time;
}
}
else
{
if (finding_aos)
{
time1 = middle_time;
}
else
{
time2 = middle_time;
}
}
if ((time2 - time1).TotalSeconds() < 1.0)
{
/*
* two times are within a second, stop
*/
running = false;
/*
* remove microseconds
*/
int us = middle_time.Microsecond();
middle_time = middle_time.AddMicroseconds(-us);
/*
* step back into the pass by 1 second
*/
middle_time = middle_time.AddSeconds(finding_aos ? 1 : -1);
}
}
/*
* go back/forward 1second until below the horizon
*/
running = true;
cnt = 0;
while (running && cnt++ < 6)
{
Eci eci = sgp4.FindPosition(middle_time);
CoordTopocentric topo = obs.GetLookAngle(eci);
if (topo.elevation > 0)
{
middle_time = middle_time.AddSeconds(finding_aos ? -1 : 1);
}
else
{
running = false;
}
}
return(middle_time);
}
public static double FindMaxElevation(CoordGeodetic user_geo, SGP4 sgp4, DateTime aos, DateTime los)
{
Observer obs = new Observer(user_geo);
bool running;
double time_step = (los - aos).TotalSeconds() / 9.0;
DateTime current_time = aos; //! current time
DateTime time1 = aos; //! start time of search period
DateTime time2 = los; //! end time of search period
double max_elevation; //! max elevation
running = true;
do
{
running = true;
max_elevation = -99999999999999.0;
while (running && current_time < time2)
{
/*
* find position
*/
Eci eci = sgp4.FindPosition(current_time);
CoordTopocentric topo = obs.GetLookAngle(eci);
if (topo.elevation > max_elevation)
{
/*
* still going up
*/
max_elevation = topo.elevation;
/*
* move time along
*/
current_time = current_time.AddSeconds(time_step);
if (current_time > time2)
{
/*
* dont go past end time
*/
current_time = time2;
}
}
else
{
/*
* stop
*/
running = false;
}
}
/*
* make start time to 2 time steps back
*/
time1 = current_time.AddSeconds(-2.0 * time_step);
/*
* make end time to current time
*/
time2 = current_time;
/*
* current time to start time
*/
current_time = time1;
/*
* recalculate time step
*/
time_step = (time2 - time1).TotalSeconds() / 9.0;
} while (time_step > 1.0);
return(max_elevation);
}
public static List <PassDetails> GeneratePassList(CoordGeodetic user_geo, SGP4 sgp4, DateTime start_time, DateTime end_time, int time_step)
{
List <PassDetails> pass_list = new List <PassDetails>();
Observer obs = new Observer(user_geo);
DateTime aos_time = null;
DateTime los_time = null;
bool found_aos = false;
DateTime previous_time = new DateTime(start_time.Ticks());
DateTime current_time = new DateTime(start_time.Ticks());
while (current_time < end_time)
{
bool end_of_pass = false;
/*
* calculate satellite position
*/
Eci eci = sgp4.FindPosition(current_time);
CoordTopocentric topo = obs.GetLookAngle(eci);
if (!found_aos && topo.elevation > 0.0)
{
/*
* aos hasnt occured yet, but the satellite is now above horizon
* this must have occured within the last time_step
*/
if (start_time == current_time)
{
/*
* satellite was already above the horizon at the start,
* so use the start time
*/
aos_time = start_time;
}
else
{
/*
* find the point at which the satellite crossed the horizon
*/
aos_time = FindCrossingPoint(
user_geo,
sgp4,
previous_time,
current_time,
true);
}
found_aos = true;
}
else if (found_aos && topo.elevation < 0.0)
{
found_aos = false;
/*
* end of pass, so move along more than time_step
*/
end_of_pass = true;
/*
* already have the aos, but now the satellite is below the horizon,
* so find the los
*/
los_time = FindCrossingPoint(user_geo, sgp4, previous_time, current_time, false);
PassDetails pd = new PassDetails();
pd.aos = aos_time;
pd.los = los_time;
pd.max_elevation = FindMaxElevation(user_geo, sgp4, aos_time, los_time);
pass_list.Add(pd);
}
/*
* save current time
*/
previous_time = current_time;
if (end_of_pass)
{
/*
* at the end of the pass move the time along by 30mins
*/
current_time = current_time.AddMinutes(30);
}
else
{
/*
* move the time along by the time step value
*/
current_time = current_time.AddSeconds(180);
}
if (current_time > end_time)
{
/*
* dont go past end time
*/
current_time = end_time;
}
}
;
if (found_aos)
{
/*
* satellite still above horizon at end of search period, so use end
* time as los
*/
PassDetails pd = new PassDetails();
pd.aos = aos_time;
pd.los = end_time;
pd.max_elevation = FindMaxElevation(user_geo, sgp4, aos_time, end_time);
pass_list.Add(pd);
}
return(pass_list);
}